The present invention concerns an electronic converter for converting an acoustic signal into a pseudo-digital signal, in particular for controlling a microprocessor, as well as a timepiece including such a converter. The invention also concerns a two-directional communication method via acoustic waves between a transmitter unit and a receiver unit.
A system for processing personal data is known from U.S. Pat. No. 5,848,027 in the name of Biometrics, Inc. This system allows, for example, the performance of an athlete, such as a runner, to be monitored. It allows to record the date and time of the time for each lap or even the final time achieved by the athlete. The system also allows the values of certain physiological parameters to be stored such as the cardiac rhythm or an electrocardiogram (ECG) which reflect the effort made by the athlete during his sporting activity. All this information will then be transmitted, via an acoustic link, to a personal computer in which the information will be processed, analysed and finally displayed on the screen of said computer.
FIG. 1 annexed to the present Patent Application shows a preferred embodiment of the aforementioned Biometric system. This system includes a portable object such as a timepiece 1, for example a digital display wristwatch, able to store data and subsequently transmit them. These data may be transmitted to a personal computer 2 in the form of acoustic xe2x80x9cbeepsxe2x80x9d generating an acoustic pressure 4 which will be picked up by a microphone 6. The timepiece may be any type of digital instrument controlled by a microprocessor and containing a piezoelectric element able to generate acoustic xe2x80x9cbeepsxe2x80x9d for data transmission. Personal computer 2 is fitted with a sound card 8 connected to microphone 6 by a cable 10. The computer is thus able to pick up acoustic pressure 4 generated by the acoustic xe2x80x9cbeepsxe2x80x9d emitted by timepiece 1. Said computer 2 may also be fitted with a display screen 2.
As shown in FIG. 2 of the present Application, timepiece 1 includes an internal microprocessor 14 which provides the timebase to said timepiece 1. Microprocessor 14 may also control a storage programme 16 co-operating with an internal random access memory. Further, a piezoelectric element 18 is able to generate at its output a pre-selected tonality. Piezoelectric element 18 is thus used to generate the acoustic xe2x80x9cbeepsxe2x80x9d similar to those generated by sound generator devices in most digital watches fitted with an alarm.
The Biometrics system described above advantageously allows personal data to be stored in a watch, then these data to be transferred by sound waves to a computer where they will be processed and analysed. This system is unfortunately not two-directional. It is thus not possible to transfer data from the computer to the watch, which considerably limits the possible applications of the Biometrics system.
Moreover, Swiss Patent No. 641 625 in the name of Seikosha, Tokyo (JP) is also known, which discloses an electric circuit for driving a piezoelectric vibrator.
FIGS. 3 and 4 annexed to the present Patent Application show, respectively by an electric diagram and by diagrams of the evolution of voltage levels as a function of time, the constitution and operating mode of a conventional drive circuit for a piezoelectric vibrator.
The electric circuit whose diagram is shown in FIG. 3 includes a coil L1, connected to the output of a transistor TR1 which is alternately xe2x80x9cONxe2x80x9d and xe2x80x9cOFFxe2x80x9d. A piezoelectric vibrator P1 is connected in parallel across coil L1. This electric circuit receives, on a connection input xe2x80x9caxe2x80x9d, a square pulsed control signal corresponding to what is shown by curve A of FIG. 4 whose abscissa represents the time xe2x80x9ctxe2x80x9d and whose ordinate represents the voltage xe2x80x9cvxe2x80x9d. From input terminal xe2x80x9caxe2x80x9d, this signal is applied to the base of transistor TR1 via a resistor R. When transistor TR1 is kept xe2x80x9cONxe2x80x9d by the control signal pulse, an electric current flows through coil L1 from a direct-current voltage source +E while connection xe2x80x9cbxe2x80x9d of piezoelectric vibrator L1 is connected to the electric circuit""s earth in accordance with what is shown by curve B of FIG. 4 (whose abscissa represents time xe2x80x9ctxe2x80x9d and whose ordinate represents voltage xe2x80x9cvxe2x80x9d).
It is to be noted that as long as transistor TR1 is xe2x80x9cONxe2x80x9d, no current flows through piezoelectric vibrator P1. The latter behaves in fact like a capacitor. The current xe2x80x9cixe2x80x9d supplied by a capacitor is equal to the product C*dE/dt, where C is the capacitance value of the capacitor, and E the voltage across its terminals. In the present case, since E is a direct-current voltage, its derivate with respect to time is zero, and the current which flows in piezoelectric vibrator P1 is also zero. It may also be noted that voltage xe2x80x9cvxe2x80x9d across the terminals of coil L1 is given by the equation v=xe2x88x92L*di/dt=E, where L is the inductance value of said coil L1, and xe2x80x9cixe2x80x9d is the current which flows through it. Consequently, the product L*di/dt is constant, which means that as long as transistor TR1 is kept xe2x80x9cONxe2x80x9d, the current which flows in coil L1 increases linearly.
At the moment that transistor TR1 passes in the xe2x80x9cOFFxe2x80x9d state at the trailing edge of each pulse of wave shape A, any accumulated energy in the coil is transmitted to the terminals of the piezoelectric vibrator, charging the latter at a much higher voltage than the supply voltage, and in the opposite direction. As can be seen on the wave shape B of FIG. 4, this oscillating voltage has a first positive pulse of great amplitude, followed by a second very damped out negative pulse. This great damping out is due to the fact that the voltage at connection point xe2x80x9cbxe2x80x9d which is connected to the collector of transistor TR1 cannot exceed, during the negative alternance, the blocking voltage of the P-N diode which forms this collector, a blocking voltage whose value is usually of the order of 0.6 volts. Thus the efficient electric energy which makes piezoelectric vibrator P1 operate is only given by the initial pulse which is of short duration, so that it is difficult to obtain high excitation of said vibrator P1. It is for this reason that one encounters the drawback of not being able to obtain a sufficiently high sound pressure level.
FIGS. 5 and 6 annexed to the present Patent Application show the solution provided by Seikosha to the aforementioned problem. FIG. 5 is a diagram representing an electric drive circuit for a piezoelectric vibrator constituting an embodiment of the Seikosha invention. FIG. 6 is a diagram of the voltage levels as a function of time at two locations of the circuit of FIG. 5.
The electric circuit whose diagram is shown in FIG. 5 includes a coil L2 and a diode D connected in series across the output of a transistor TR2. A piezoelectric vibrator P2 is connected in parallel across this series connection.
At the moment when transistor TR2 passes to the xe2x80x9cOFFxe2x80x9d state at the trailing edge of each pulse of the square control signal (curve A, FIG. 6), a voltage is induced in coil L2 and is applied, via diode D which remains polarised in the conductive direction, to the terminals of piezoelectric vibrator P2 (curve B, FIG. 6). The voltage across the terminals of vibrator P2 then remains blocked at its maximum level, since, at the beginning of the reverse voltage pulse in coil L2, diode D is polarised in the non conductive direction and blocks the return of the current. As can be seen by comparing voltage levels B of FIGS. 4 and 6, the energy which is provided to piezoelectric vibrator P2 is much greater than that which was provided to piezoelectric vibrator P1 of the prior art.
Consequently, the Seikosha invention allows a substantial increase in the acoustic pressure level. However, this invention does not suggest the use of a piezoelectric vibrator for receiving and digitising of sound wave trains.
The object of the present invention is to overcome the above problems and drawbacks as well as others by providing an electronic converter for converting an acoustic signal into a pseudo-digital signal for operating a drive circuit for a piezoelectric vibrator in the manner of an acoustic wave sensor, and converting these wave trains into digital pulses.
According to a first aspect, the present invention therefore concerns the use of a sound generator circuit including a piezoelectric vibrator as an acoustic wave receiver.
According to a complementary feature of the invention, the sound generator circuit includes switching means arranged to be switched on and off upon receiving a control signal, as well as a circuit branch wherein a coil and a diode are mounted in series, a resistor and a piezoelectric vibrator being connected in parallel across said circuit branch.
As a result of these features, it is possible to use as acoustic wave receiver an electric circuit, which, originally, was solely designed to drive a piezoelectric vibrator used as a sound generator in electronic watches fitted with an alarm device. This object is achieved without it being necessary to modify the vibrator drive circuit, which means that substantial savings can be made in terms of manufacturing costs, and that a reliable, compact circuit can be provided.
According to a second aspect, the present invention concerns an electronic converter for converting an acoustic signal into a pseudo-digital signal, said electronic converter including a sound generator circuit provided with a piezoelectric vibrator as well as means supplying a reference voltage, characterised in that it further includes comparison means which compare the reference voltage to the voltage generated by the piezoelectric vibrator when the latter picks up an acoustic wave, said comparison means generating a pseudo-digital signal when the voltage generated by said vibrator exceeds said reference voltage.
As a result of these other features, one can not only generate a sound, but also pick up this sound and convert it into a logic voltage able to be used to control a microprocessor. It therefore becomes possible to envisage exchanging all types of data by acoustic waves between two distant objects, such as for example, two wristwatches or a wristwatch and a computer, using only the addition of a comparator circuit to the piezoelectric vibrator drive circuit. A two-directional communication system via acoustic waves is thereby obtained which is much simpler and much more compact than the wireless communication systems, for example via infrared or radio-frequency, which are currently known.
The present invention also concerns a timepiece including a converter circuit as described above.
The present invention finally concerns a two-directional communication method via acoustic waves between an emitter unit and a receiver unit, each of these two units including a microprocessor and an electronic converter, said converter including a sound generator circuit provided with a piezoelectric vibrator as well as means supplying a reference voltage, the method being characterised in that:
the sound generator circuit includes switching means arranged to be switched on and off on receiving a pulsed control signal;
the electronic converter also includes comparison means which compare the reference voltage to a voltage generated by the piezoelectric vibrator when the latter picks up an acoustic wave, these comparison means generating a pseudo-digital signal formed of a succession of logic pulses when the voltage generated by said vibrator exceeds the reference voltage;
as long as the emitter and receiver are idle, the microprocessor of the receiver waits for a sound signal;
as soon as the emitter sends the first of a series of successive acoustic xe2x80x9cbeepsxe2x80x9d, the microprocessor of the receiver instructs a time counter to start and begins to count the number of logic pulses generated by the comparison means, so that said microprocessor can calculate the number of pulses received in a given time interval, and determine by reading in a counter whether the logic level is xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d.
According to a complementary feature of the invention, the method is characterised in that each xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d logic level corresponds to a long xe2x80x9cbeepxe2x80x9d or a short xe2x80x9cbeepxe2x80x9d, two successive acoustic xe2x80x9cbeepsxe2x80x9d being separated by a silent period during which the emitter does not emit.
Other features and advantages of the present invention will appear more clearly upon reading the following detailed description of an embodiment example of the electronic converter according to the invention, this example being given purely by way of non-limiting illustration, in conjunction with the annexed drawings, in which:
FIG. 1 which has already been cited, shows a timepiece able to store personal data, then transmit these data to a computer via a sound link;
FIG. 2 which has already been cited, is a block diagram of a timepiece as shown in FIG. 1, including a data processing programme, as well as means for storing and transmitting said data;
FIGS. 3 and 4, which have already been cited, show respectively via an electric diagram and via voltage level evolution diagrams as a function of time, the constitution and operation mode of a first embodiment of a drive circuit for a piezoelectric vibrator;
FIG. 5, which has already been cited, shows the diagram of a second embodiment of a drive circuit for a piezoelectric vibrator;
FIG. 6, which has already been cited, is a voltage level diagram as a function of time at two locations of the circuit of FIG. 5;
FIG. 7 shows an electric diagram of a circuit for converting an acoustic signal into a pseudo-digital signal according to the present invention;
FIG. 8 shows the voltage levels as a function of time at two locations of the circuit of FIG. 7;
FIG. 9 shows the voltage levels as a function of time at two locations of the circuit of FIG. 7 when this circuit is used as a sound wave receiver;
FIG. 10 shows an electric diagram of two converter circuits according to the present invention, arranged side by side in order to determine the frequency transfer function of the acoustic system formed by these two converters;
FIG. 11 is a graphic diagram of the frequency transfer function of the system of FIG. 10;
FIG. 12 is a schematic diagram of two electronic wristwatches which exchange data with each other via sound waves;
FIGS. 13A and 13B respectively show the envelope of the sound signal emitted by an emitter watch, as well as the square pulsed control voltage applied to the switching transistor of said watch;
FIG. 14 shows the voltage levels at the connection point of the piezoelectric vibrator and at the output of the analogue-digital converter in the receiver watch; and
FIG. 15 is a graphic diagram of the FSK modulation coding principle.